Tracking intermediate changes in database data

ABSTRACT

Systems, methods, and devices for tracking a series of changes to database data are disclosed. A method includes executing a transaction to modify data in a micro-partition of a table of a database by generating a new micro-partition that embodies the transaction. The method includes associating transaction data with the new micro-partition, wherein the transaction data comprises a timestamp when the transaction was fully executed, and further includes associating modification data with the new micro-partition that comprises an indication of one or more rows of the table that were modified by the transaction. The method includes joining the transaction data with the modification data to generate joined data and querying the joined data to determine a listing of intermediate modifications made to the table between a first timestamp and a second timestamp.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.16/182,216, filed on Nov. 6, 2018, the contents of which areincorporated herein in their entirety.

TECHNICAL FIELD

The present disclosure relates systems, methods, and devices fordatabases and more particularly relates to tracking intermediate changesto database data.

BACKGROUND

Databases are widely used for data storage and access in computingapplications. Databases may include one or more tables that include orreference data that can be read, modified, or deleted using queries.Databases can store anywhere from small to extremely large sets of datawithin one or more tables. This data can be accessed by various users inan organization or even be used to service public users, such as via awebsite or an application program interface (API). Both computing andstorage resources, as well as their underlying architecture, can play asignificant role in achieving desirable database performance.

Database data can be modified by various commands, including insert,delete, and update commands that modify one or more rows in a databasetable. It can be costly to track such modifications and to determinedelta information between a first set of database data and a second setof database data. Systems, methods, and devices for efficient trackingof changes made to database data are disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present disclosureare described with reference to the following figures, wherein likereference numerals refer to like parts throughout the various figuresunless otherwise specified.

FIG. 1 is a block diagram illustrating modifications made to tableversions, according to one embodiment;

FIG. 2 is a block diagram illustrating a delete command performed on amicro-partition of a database, according to one embodiment;

FIG. 3 is a block diagram illustrating an insert command performed on amicro-partition of a database, according to one embodiment;

FIG. 4 is a block diagram illustrating an update command performed on amicro-partition of a database, according to one embodiment;

FIG. 5 is a block diagram illustrating a database system having adatabase service manager, according to one embodiment;

FIG. 6 is a block diagram illustrating components of a database servicemanager, according to one embodiment;

FIG. 7 is a block diagram illustrating components of a change trackingmanager, according to one embodiment;

FIG. 8 is a schematic flow chart diagram illustrating a method fortracking changes to database data, according to one embodiment;

FIG. 9 is a schematic flow chart diagram illustrating a method fortracking changes to database data, according to one embodiment; and

FIG. 10 is a block diagram depicting an example computing deviceconsistent with at least one embodiment of processes and systemsdisclosed herein.

DETAILED DESCRIPTION

Systems, methods, and devices for tracking a series of changes todatabase data and for returning a comprehensive change tracking summaryfor a database table are disclosed. Database change tracking can returna summary of what rows have changed in a database table and how thoserows have changed. A delta may be returned for a database that indicateswhich rows have changed and how they have changed between two timestampsand does not include information on all intermediate changes thatoccurred between the two timestamps. A comprehensive change trackingsummary may be returned that indicates how data has changed between twotimestamps and includes all intermediate changes that occurred betweenthe first timestamp and the second timestamp.

Change tracking is historically very costly and requires significantresources and storage capacity. Database systems are traditionally builtusing a transaction log that embodies all changes made in the database.The transactional log is normally used to make transactional changesatomic and durable and may further be used in recover in an instancewhere the database system crashes and information must be restored. Thetransactional includes all changes that have occurred on the databaseand may be used to reconstruct those changes. However, the transactionallog approach requires significant system resource because items must bestored using a scan of the log because there is no random-access storagestructure to speed up the process of reconstructing the database.Further, the transactional log itself is physical and must be parsed andapplied to a page structure to provide whole row images and changes.

In an alternative approach known in the art, temporal information aboutdata changes may be stored in two transactional timestamp columns withina database table. The transactional timestamp columns indicatetransactional times when a row was valid. An internal history table maybe generated that stores updated data information with the timestampsfrom the transactional timestamp columns. Updates and deletes copy thevalues of changed rows into the internal history table and update thetransactional timestamp columns to mark the valid transactional lifetimeof rows. When the historical or changed data set is required, a currenttable and the internal history table must be joined to gather the deltaor historical information between two transactional time points. Themaintenance of the transactional timestamp columns and the internalhistory table adds significant overhead to the database transactions.Additionally, delta queries must join the information from two tableswhen requested.

A comprehensive change tracking summary is historically generated bydetermining a modification that has occurred between all sequentialpairs of transactions that occur on the table. For example, amodification will be determined between a timestamp zero and a timestampone; a change will be determined between a timestamp one and a timestamptwo; a change will be determined between a timestamp two and a timestampthree, and so forth. The modifications may be determined by comparingthe data within the table at the timestamp zero and at the timestampone, and so forth for each sequential pair of transactions in a relevanttime period. This can require enormous sums of data to be stored in thedatabase and can be extremely costly and time intensive to perform. Theseries of modification may then be reported to indicate allmodifications that occurred on the table in a relevant time period wheresuch modification includes, for example, updates, deletes, inserts, ormerges on the database data.

Systems, methods, and devices disclosed herein provide a low-cost meansfor generating a comprehensive change tracking summary that includes allmodifications that have occurred on a database table in a relevant timeperiod. Such systems, methods, and devices enable a single query to berun on transactional information to return a comprehensive listing ofmodifications that have occurred on a table. This significantly reducesthe storage capacity and computing resources that are required foranalyzing database transactions and/or modifications over a time period.

A database table may be altered in response to a data manipulation (DML)statement such as an insert command, a delete command, an updatecommand, a merge command, and so forth. Such modifications may bereferred to as a transaction that occurred on the database table. In anembodiment, each transaction includes a timestamp indicating when thetransaction was received and/or when the transaction was fully executed.In an embodiment, a transaction includes multiple alterations made to atable, and such alterations may impact one or more micro-partitions inthe table.

A database table may store data in a plurality of micro-partitions,wherein the micro-partitions are immutable storage devices. When atransaction is executed on a such a table, all impacted micro-partitionsare recreated to generate new micro-partitions that reflect themodifications of the transaction. After a transaction is fully executed,any original micro-partitions that were recreated may then be removedfrom the database. A new version of the table is generated after eachtransaction that is executed on the table. The table may undergo manyversions over a time period if the data in the table undergoes manychanges, such as inserts, deletes, updates, and/or merges. Each versionof the table may include metadata indicating what transaction generatedthe table, when the transaction was ordered, when the transaction wasfully executed, and how the transaction altered one or more rows in thetable. The disclosed systems, methods, and devices for low-cost tableversioning may be leveraged to provide an efficient means for generatinga comprehensive change tracking summary that indicates all intermediatechanges that have been made to a table between a first timestamp and asecond timestamp.

Change tracking information can be stored as metadata in a database.This metadata describes the data that is stored in database tables ofcustomers but is not actually the stored table data. Metadata can getvery large, especially if there are large database tables of manycustomers. Current database systems have severe limitations handlinglarge amounts of metadata. Current database systems store metadata inmutable storage devices and services, including main memory, filesystems, and key-value stores. These devices and services allow themetadata to be updated data in-place. If a data record changes, it maybe updated with the new information and the old information isoverwritten. This allows databases to easily maintain mutable metadataby updating metadata in-place.

However, these mutable storage devices and services have limitations.The limitations are at least two-fold. First, mutable storage devicessuch as main memory and file systems have a hard limit in terms ofstorage capacity. If the size of the metadata exceeds these limits, itis impossible to store more metadata there. Second, mutable storageservices such as key-value stores perform poorly when reading largevolumes of metadata. Reading data is performed using range scans, whichtake a long time to finish. In practice, range scans can take manyminutes or even approach an hour to complete in large scale deployments.

These limitations make it impossible to store large amounts of metadatain existing mutable storage devices and services. Systems, methods, anddevices disclosed herein provide for improved metadata storage andmanagement that includes storing metadata in immutable (non-mutable)storage such as micro-partitions. As used herein, immutable ornon-mutable storage includes storage where data cannot or is notpermitted to be overwritten or updated in-place. For example, changes todata that is located in a cell or region of storage media may be storedas a new file in a different, time-stamped, cell or region of thestorage media. Mutable storage may include storage where data ispermitted to be overwritten or updated in-place. For example, data in agiven cell or region of the storage media can be overwritten when thereare changes to the data relevant to that cell or region of the storagemedia.

In one embodiment, metadata is stored and maintained on non-mutablestorage services in the cloud. These storage services may include, forexample, Amazon S3 ®, Microsoft Azure Blob Storage®, and Google CloudStorage®. Many of these services do not allow to update data in-place(i.e., are non-mutable or immutable). Data files may only be added ordeleted, but never updated. In one embodiment, storing and maintainingmetadata on these services requires that, for every change in metadata,a metadata file is added to the storage service. These metadata filesmay be periodically consolidated into larger “compacted” or consolidatedmetadata files in the background.

In an embodiment, all data in tables is automatically divided into animmutable storage device referred to as a micro-partition. Themicro-partition may be considered a batch unit where eachmicro-partition has contiguous units of storage. By way of example, eachmicro-partition may contain between 50 MB and 500 MB of uncompresseddata (note that the actual size in storage may be smaller because datamay be stored compressed). Groups of rows in tables may be mapped intoindividual micro-partitions organized in a columnar fashion. This sizeand structure allow for extremely granular pruning of very large tables,which can be comprised of millions, or even hundreds of millions, ofmicro-partitions. Metadata may be automatically gathered about all rowsstored in a micro-partition, including: the range of values for each ofthe columns in the micro-partition; the number of distinct values;and/or additional properties used for both optimization and efficientquery processing. In one embodiment, micro-partitioning may beautomatically performed on all tables. For example, tables may betransparently partitioned using the ordering that occurs when the datais inserted/loaded.

A detailed description of systems and methods consistent withembodiments of the present disclosure is provided below. While severalembodiments are described, it should be understood that this disclosureis not limited to any one embodiment, but instead encompasses numerousalternatives, modifications, and equivalents. In addition, whilenumerous specific details are set forth in the following description toprovide a thorough understanding of the embodiments disclosed herein,some embodiments may be practiced without some or all these details.Moreover, for the purpose of clarity, certain technical material that isknown in the related art has not been described in detail to avoidunnecessarily obscuring the disclosure.

In an embodiment, a method for tracking intermediate changes to databasedata is disclosed. The method includes executing a transaction to modifydata in a micro-partition of a table of a database by generating a newmicro-partition that embodies the transaction. The method includesassociating transaction data with the new micro-partition, wherein thetransaction data comprises a timestamp when the transaction was fullyexecuted. The method includes associating modification data with the newmicro-partition that comprises an indication of one or more rows of thetable that were modified by the transaction. The method includes joiningthe transaction data with the modification data to generate joined data.The method includes querying the joined data to determine a listing ofintermediate modifications made to the table between a first timestampand a second timestamp.

In an embodiment, the transaction data includes information on thetransaction that caused the new micro-partition to be generated. In animplementation where a plurality of new micro-partitions is generatedbased on one transaction, the transaction data will be associated witheach of the new micro-partitions. The transaction data includes, forexample, an identity of a user or account that initiated thetransaction, a timestamp when the transaction was requested, a timestampwhen execution of the transaction began, a timestamp when execution ofthe transaction was completed, a listing of all rows that were modifiedby the transaction and how those rows were modified, a listing ofmicro-partitions that were generated and/or removed based on thetransaction, and any other suitable information relevant to thetransaction. The transaction data may be stored within the newmicro-partition as metadata.

In an embodiment, the modification data includes information on whatrows were modified by a transaction, what micro-partitions were modifiedby a transaction, how the rows and/or micro-partitions were modified bythe transaction, information on prior modifications on the table, and soforth. The modification data may include a lineage of modifications madeon the table since the table was initially generated, or since aparticular time. The modification data may include a listing of tableversions of the table, including all micro-partitions that are currentlypart of or were historically part of the table. The modification datamay be stored within the new micro-partition as metadata.

In an embodiment, the transaction data and the modification data arejoined to generate joined data. The joined data indicates at least (a)what transaction caused a modification to the table; and (b) how thetable was modified. The joined data may be queried to determine alisting of intermediate modifications that have been made to the tablebetween a first timestamp and a second timestamp. The listing ofintermediate modifications may include a listing of all transactionsthat have been executed on the table and how those transactions modifiedthe table. The listing of intermediate modifications includes tablemodifications that are later reversed by subsequent transactions betweenthe first timestamp and the second timestamp.

Querying the listing of intermediate modifications provides an efficientand low-cost means for determining a comprehensive listing ofincremental changes made to a database table between two points in time.This is superior to methods known in the art where each of a series ofsubsequent table versions must be manually compared to determine how thetable has been modified over time. Such methods known in the art requireextensive storage resources and computing resources to execute.

In an embodiment, a table version history is generated and includes oneor more change tracking columns stored within the micro-partition and/orthe new micro-partition. The one or more change tracking columns mayinclude information indicating one or more of: a prior micro-partitionname for a row value, a prior row identification for a row value, anaction taken on a row value, whether a row value was updated, a log ofchanges made to a row or row value, a lineage for a row indicating oneor more changes made to the row over a time period, a listing oftransactions that have initiated a modification to a row, and any othersuitable information that may indicate change made to a row ormicro-partition or a historical listing of changes that have been madeto a row or micro-partition in a table.

In an embodiment, file metadata is stored within metadata storage. Thefile metadata contains table versions and information about each tabledata file. The metadata storage may include mutable storage (storagethat can be over written or written in-place), such as a local filesystem, system, memory, or the like. In one embodiment, themicro-partition metadata consists of two data sets: table versions andfile information. The table versions data set includes a mapping oftable versions to lists of added files and removed files. Fileinformation consists of information about each micro-partition,including micro-partition path, micro-partition size, micro-partitionkey id, and summaries of all rows and columns that are stored in themicro-partition, for example. Each modification of the table creates newmicro-partitions and new micro-partition metadata. Inserts into thetable create new micro-partitions. Deletes from the table removemicro-partitions and potentially add new micro-partitions with theremaining rows in a table if not all rows in a micro-partition weredeleted. Updates remove micro-partitions and replace them with newmicro-partitions with rows containing the updated records.

In one embodiment, metadata may be stored in metadata micro-partitionsin immutable storage. In one embodiment, a system may write metadatamicro-partitions to cloud storage for every modification of a databasetable. In one embodiment, a system may download and read metadatamicro-partitions to compute the scan set. The metadata micro-partitionsmay be downloaded in parallel and read as they are received to improvescan set computation. In one embodiment, a system may periodicallyconsolidate metadata micro-partitions in the background. In oneembodiment, performance improvements, including pre-fetching, caching,columnar layout and the like may be included. Furthermore, securityimprovements, including encryption and integrity checking, are alsopossible with metadata files with a columnar layout.

FIG. 1 illustrates a schematic block diagram of a table history 100 withmultiple table versions. The example table history 100 illustrates threetable versions, namely table version 1, table version 2, and tableversion 3. Table version 1 includes data in the form of threemicro-partitions (MPs), namely micro-partition 1 (MP1), micro-partition2 (MP2), and micro-partition 3 (MP3). A first transaction 102 isexecuted on table version 1 to generate table version 2. The firsttransaction 102 includes deleting rows in MP2 to generate a newmicro-partition 4 (MP4) and deleting the original MP2. The firsttransaction 102 executed on table version 1 generates table version 2which includes the original MP1 and MP3 along with the newly generatedMP4. As a result of the first transaction 102, MP2 has been removed fromthe table as reflected in table version 2. A second transaction 104 isexecuted on table version 2 to generate table version 3. The secondtransaction 104 includes inserting new rows such that micro-partition 5(MP5) is generated and MP3 is removed from the table. Table version 3includes the original MP1, the MP4 generated as a result of the firsttransaction 102, and MP5 generated as a result of the second transaction104. The MP2 was removed as a result of the first transaction 102 andthe MP3 was removed from the table as a result of the second transaction104.

As illustrated in FIG. 1, a database table may store database data inone or more micro-partitions, wherein the micro-partitions constituteimmutable storage devices. When a change or modification is executed onthe table, the affected micro-partitions are removed, and newmicro-partitions are created that reflect the change. In an embodiment,the original unmodified micro-partition is not removed but is alsostored with the new micro-partition. The change may include any commandthat impacts one or more rows in the table, including for example, adelete command, an insert command, an update command, and/or a mergecommand.

In an embodiment, a comprehensive change tracking summary may bedetermined that indicates all changes that have been made between, forexample, table version 1 and table version 3. A comprehensive changetracking summary for the implementation illustrated in FIG. 1 willindicate that a first transaction 102 caused rows to be deleted from MP2and caused MP4 to be generated without those rows. The summary willfurther indicate that a second transaction 104 caused new rows to beinserted into the table, caused MP3 to be removed, and caused MP5 to begenerated with those new rows. The comprehensive change tracking summaryindicates all transactions that occur on the table, when thosetransactions occurred, and how those transactions impacted the table.

In an embodiment, a table history is updated only if a transaction isfully completed. Therefore, if a transaction is initiated but is notfully completed, the table history will not be updated to include thattransaction. For example, if a transaction is initiated to deletecertain rows of an original micro-partition, a new micro-partition willbe generated that includes all original rows in the originalmicro-partition except for those that should be deleted based on adelete command. If the transaction is not completed, i.e. if the newmicro-partition is not fully generated, then the table history will notbe updated to indicate that the transaction occurred.

In an embodiment, the table history is stored in a metadata column thatincludes a micro-partition lineage storing a lineage of micro-partitionnames over a time period. The metadata column may further include a rowlineage storing a lineage of ordinal numbers for a given row over a timeperiod. Such values are NULL when a table is first created or when a newrow is generated within the table. When a new row is generated, thestored values will be NULL, and the actual logical value may be derivedfrom the name of the micro-partition that the row is stored within andthe rank of the row within that micro-partition.

In an embodiment, when a row is copied into a new micro-partition aspart of a DML query execution, and if the value for the row is NULL, thelineage of the row is materialized by replacing the value with theapplicable micro-partition name and the applicable rank of the rowwithin that micro-partition. When a row is copied into a newmicro-partition and the value of the row is not NULL, the name of therow is copied over into the new micro-partition.

FIGS. 2-4 illustrate exemplary embodiments of delete, insert, and updatecommands that may be executed on a database table. It should beappreciated that the table schemas illustrated in FIGS. 2-4 areillustrative and include simple values to represent rows and columnsthat may be included in a database table.

FIG. 2 illustrates a block diagram of an example delete command 200 anda resulting delta 210 that may be returned after the delete command 200is complete. Micro-partition 2 (MP2) as illustrated in FIG. 2 includesfour columns. Column 1 includes entries for row numbers that areprimarily used for identification purposes. Column 2 includes entriesfor row values that may include any value depending on the subject orpurpose of the database table. The metadata name column includes tablehistory information about which micro-partition the data originated fromor was last located within. The metadata row column includes tablehistory information about which row the data originated from or waslocated within.

As illustrated in FIG. 2, the delete command 200 is performed on MP2 anddeletes rows 2 and 3 from MP2 to generate the new MP4. As an example, asillustrated in FIG. 2, MP2 includes four rows—namely rows 1, 2, 3, and4. It should be appreciated that a micro-partition may include anynumber of rows and may often include thousands of rows in a singlemicro-partition. The values for each of the rows in MP2 are listed asvalue1, value2, value3, and value4 for the four rows by way of examplebut it should be appreciated the value may include any suitable value aspertinent to the database. In the original and unmodified MP2, themetadata name for each of the four rows is “NULL (MP2)” indicating thedata is original to that micro-partition and does not yet have anychange history. Similarly, the metadata row column for MP2 is NULL andindicates the original row number because the data is original to MP2and does not yet have a change tracking history.

MP4 is generated based on the delete command 200 performed on MP2 thatdeleted rows 2 and 3 as illustrated in FIG. 2. MP4 now only includesrows 1 and 4 having values value1 and value4, respectively. The metadataname for each of rows 1 and 4 is “MP2” indicating the row dataoriginated or was last located within MP2. The metadata row for each ofrows 1 and 4 is 1 and 4, respectively, indicating where the rows werelast located.

A delta 210 may be determined after the delete command 200 is performedon a table. In an embodiment, a timestamp is attached to eachtransaction that occurs on the table. If the transaction is fullycompleted, then the timestamp is further attached to the change trackinghistory for that transaction. Attaching the timestamp to the changetracking history enables the system to know when a table was changed bya certain transaction and when a certain change occurred on any of aplurality of rows in the table.

The delta 210 illustrated in FIG. 2 determines a difference or a changethat occurred between MP2 and MP4. In various embodiments the delta 210may determine a total change that has occurred between any twotimestamps, even if many transactions have occurred on the data betweenthose two timestamps and the data has been changed multiple times. Thedelta 210 provides an indication of a total change between twotimestamps without providing information on any intermediate changesthat occurred between a first timestamp and a second timestamp.

The delta 210 includes four columns, namely a column 1 and column 2(similar to those shown in MP2 and MP4) along with a metadata actioncolumn and a metadata is update column. Column 1 indicates that rows 2and 3 have been altered between the first timestamp and the secondtimestamp. Column 2 indicates that the values of rows 2 and 3 are value2and value3, respectively. In various embodiments, where the values ofrows 2 and 3 may have changed one or more times between the firsttimestamp and the second timestamp, Column 2 may indicate the originalvalue or the most recent value. The metadata action column indicatesthat rows 2 and 3 underwent a DELETE command. The metadata is updatecolumn indicates whether the metadata was updated. In the delta 210illustrated in FIG. 2, the metadata is update column returns a FALSEbecause the rows did not undergo an update (but were instead deleted).

In an embodiment, a table history is generated that includes alltransactions that have been initiated against the table. Suchtransactions may include, for example, data manipulation language (DML)commands such as delete, insert, merge, or update commands initiated ona micro-partition. The table history may be dynamically updated toreflect all deleted or inserted rows on table for an interval oftransaction time. The table history may include a list of DML statementssorted by transaction time, where each transaction includes a timestamp.In an embodiment, it is assumed that all DML statements will delete,insert, and/or update rows at the same time.

In an embodiment, a table history may be determined by retrieving a listof added and removed micro-partitions between two transactions. For eachgiven micro-partition, a lineage sequence of dependencies may begenerated that indicates which rows have been updated, how those rowswere updated, and what transaction caused each update. A delta may bedetermined by requesting a changeset between two timestamps in thelineage. The delta may return a listing of all added micro-partitionsand all removed micro-partitions between the two timestamps. The listingmay be consolidated by removing those micro-partitions that appear onboth the list of added micro-partitions and on the list of removedmicro-partitions. This may be accomplished by performing anti-join onthe lists of added and removed micro-partitions.

In an embodiment, the row granularity changes between added and removedmicro-partitions is determined. In such an embodiment, a full outer joinis performed between a rowset of added micro-partitions and a rowset ofremoved micro-partitions on a metadata partition and metadata row numbercolumns. When the resulting joined rowset includes NULL values for themetadata columns in the data from the added rowset, this indicates thoserows represent DELETEs. If the values for the metadata columns in thedata from the inserted rowset are NULL, this indicates those rowsrepresent INSERTs. If the metadata columns originating from the addedand removed rowsets are both NULL, this indicates the rows werepotentially updated, and comparing the original data columns will resultin the information indicating whether the rows were actually modified.

Further in an embodiment, a row granularity list of changes may bedetermined between any two transaction times for a given table. Aside-by-side representation may be generated that may be easily used ina merge statement by checking which part of data is present. A tablevalued function may be utilized to query the table history for a giventable (or a materialized view). Further, a SQL statement may be utilizedby referring the INSERTED or DELETED columns in a changeset to return anindication of which rows in the table have been inserted or deleted.

FIG. 3 illustrates a block diagram of an example insert command 300 anda resulting delta 310 that may be returned after the insert command 300is complete. FIG. 3 begins with an exemplary micro-partition 3 (MP3)that undergoes an insert command 300 to generate micro-partition 5(MP5). The insert command 300 inserts rows 17 and 18 into MP3. As anexample, embodiment, MP3 includes three rows, namely rows 21, 22, and 23having values of value21, value22, and value23, respectively. Themetadata name is NULL (MP3) for each of the three rows because there isnot yet a change tracking history for the rows that indicates where therows originated or were last stored. NULL( ) notation indicates that thevalues for the metadata columns are NULL when rows are first insertedinto the table. The NULL( ) notation can reduce overhead. When valuesfor a row are copied into a new micro-partition, the rank of the row isnotated in the NULL( ) notation, such that the first row is NULL(1), thesecond row is NULL(2), the third row is NULL(3), and so forth.

MP5 is generated based on the insert command 300 and now includes rows17 and 18. The values for rows 17 and 18 are value17 and value 18,respectively, because rows 17 and 18 were inserted into MP5 and thoseare the assigned values for the rows. The values for rows 21, 22, and 23have not changed. The metadata name information for rows 21, 22, and 23is “MP3” because the data originated from or was last stored inmicro-partition 3. The metadata row information for rows 21, 22, and 23is 1, 2, and 3, respectively, because rows 21, 22, and 23 wereoriginally or last stored in rows 1, 2, and 3 in micro-partition 3. Themetadata name information and the metadata row information for rows 17and 18 is “NULL” because the rows originated in MP5 and do not yet haveany change tracking history information.

The delta 310 for the insert command 300 illustrates the total changemade between a first timestamp and a second timestamp. As illustrated inFIG. 2, the delta 310 illustrates the change that occurred between MP5and MP3. It should be appreciated that in alternative embodiments orimplementations, a delta may indicate a total change or modificationthat occurred on a table between any two timestamps without indicatingincremental changes that occurred on the table.

The delta 310 includes rows 17 and 18 having value17 and value18,respectively because rows 17 and 18 were added to MP3 because of theinsert command 300. The metadata action is “INSERT” for rows 17 and 18because an insert command 300 was the transaction that caused amodification to the rows. The metadata is update information is “FALSE”for rows 17 and 18 because the rows were not updated but were insteadinserted.

FIG. 4 illustrates a block diagram of an example update command 400 anda resulting delta 410 that may be returned after the update command 400is complete. In the example embodiment illustrated in FIG. 4,micro-partition 78 (MP78) is updated to generate micro-partition 91(MP91). The update command 400 updates rows 1 and 4 to new values. MP78includes rows 1, 2, 3, and 4 having values of value1, value2, value3,and value4, respectively. The metadata name information is “NULL (MP78)for each of the rows because there is not yet change tracking historyfor the rows indicating where the rows were last stored. The metadatarow information for each of the rows is NULL because there is not yetchange tracking history for the rows indicating which row the valueswere last stored.

MP91 includes rows 1, 2, 3, and 4. However, due to the update command400, row 1 now has a value of VALUE11 and row 4 now has a value ofVALUE44. The metadata name information for each of rows 1, 2, 3, and 4is “MP78” because the values originated from or were last stored inMP78. The metadata row information for rows 1 is “1” because that valuewas last stored in row 1 in MP78. Similarly, for rows 2, 3, and 4, themetadata row information is “2”, “3”, and “4”, respectively. When rows1, 2, 3, and 4 were copied over to the new MP91 the ordinal position(also referred to as “rank”) of the rows was also copied over from theoriginal MP78.

The delta 410 indicates the change between a first timestamp and asecond timestamp. As illustrated in FIG. 4, the delta 410 indicates atotal change between MP78 and MP91 due to the update command 400. Thedelta 410 indicates that rows 1 and 4 that had a value of“value1” and“value2”, respectively, were deleted. The delta 410 indicates that rows1 and 4 that have a value of “VALUE 11” and “VALUE44”, respectively,were inserted. The metadata is update information is “TRUE” for all rowsbecause an update command 400 was performed on the rows. As indicated inthe delta 410, when an update command is performed, the original row isdeleted, and a new row is inserted to carry out the command.

In an embodiment, each delta 210, 310, 410 may be utilized to determinea comprehensive change tracking summary for a table between a firsttimestamp and a second timestamp. The delta information may be stored asmetadata in a change tracking column in each new micro-partition that isgenerated in the table. The delta information may be queried todetermine the comprehensive change tracking summary for the table.

Turning to FIG. 5, a block diagram is shown illustrating a processingplatform 500 for providing database services, according to oneembodiment. The processing platform 500 includes a database servicemanager 502 that is accessible by multiple users 504, 506, and 508. Thedatabase service manager 502 may also be referred to herein as aresource manager or global services. In some implementations, databaseservice manager 502 can support any number of users desiring access todata or services of the processing platform 500. Users 504-508 mayinclude, for example, end users providing data storage and retrievalqueries and requests, system administrators managing the systems andmethods described herein, software applications that interact with adatabase, and other components/devices that interact with databaseservice manager 502. In a particular embodiment as illustrated herein,the users 504-508 may initiate changes to database data and may requesta delta for a database table.

The database service manager 502 may provide various services andfunctions that support the operation of the systems and componentswithin the processing platform 500. Database service manager 502 hasaccess to stored metadata associated with the data stored throughoutdata processing platform 500. The database service manager 502 may usethe metadata for optimizing user queries. In some embodiments, metadataincludes a summary of data stored in remote data storage systems as wellas data available from a local cache (e.g., a cache within one or moreof the clusters of the execution platform 512). Additionally, metadatamay include information regarding how data is organized in the remotedata storage systems and the local caches. Metadata allows systems andservices to determine whether a piece of data needs to be processedwithout loading or accessing the actual data from a storage device.

As part of the data processing platform 500, metadata may be collectedwhen changes are made to the data using a data manipulation language(DML), which changes may be made by way of any DML statement. Examplesof manipulating data may include, but are not limited to, selecting,updating, changing, merging, and inserting data into tables. As part ofthe processing platform 500, micro-partitions may be created, and themetadata may be collected on a per file and a per column basis. Thiscollection of metadata may be performed during data ingestion or thecollection of metadata may be performed as a separate process after thedata is ingested or loaded. In an implementation, the metadata mayinclude a number of distinct values; a number of null values; and aminimum value and a maximum value for each file. In an implementation,the metadata may further include string length information and ranges ofcharacters in strings.

In one embodiment, at least a portion of the metadata is stored inimmutable storage such as a micro-partition. For example, the metadatamay be stored on the storage platform 514 along with table data. In oneembodiment, the same or separate cloud storage resources that are usedfor table data may be allocated and used for the metadata. In oneembodiment, the metadata may be stored in local immutable storage. Inone embodiment, information about the metadata in immutable storage, orinformation about metadata files stored in immutable storage, is storedin mutable storage 510. The information about metadata may be referencedfor locating and accessing the metadata stored in immutable storage. Inone embodiment, systems with metadata storage may be restructured suchthat the metadata storage is used instead to store information aboutmetadata files located in immutable storage.

Database service manager 502 is further in communication with anexecution platform 512, which provides computing resources that executevarious data storage and data retrieval operations. The executionplatform 512 may include one or more compute clusters. The executionplatform 512 is in communication with one or more data storage devices516, 518, and 520 that are part of a storage platform 514. Althoughthree data storage devices 516, 518, and 520 are shown in FIG. 5, theexecution platform 512 is capable of communicating with any number ofdata storage devices. In some embodiments, data storage devices 516,518, and 520 are cloud-based storage devices located in one or moregeographic locations. For example, data storage devices 516, 518, and520 may be part of a public cloud infrastructure or a private cloudinfrastructure, or any other manner of distributed storage system. Datastorage devices 516, 518, and 520 may include hard disk drives (HDDs),solid state drives (SSDs), storage clusters, or any other data storagetechnology. Additionally, the storage platform 514 may include adistributed file system (such as Hadoop Distributed File Systems (HDFS),object storage systems, and the like.

In some embodiments, the communication links between database servicemanager 502 and users 504-508, mutable storage 510 for information aboutmetadata files (i.e., metadata file metadata), and execution platform512 are implemented via one or more data communication networks and maybe assigned various tasks such that user requests can be optimized.Similarly, the communication links between execution platform 512 anddata storage devices 516-520 in storage platform 514 are implemented viaone or more data communication networks. These data communicationnetworks may utilize any communication protocol and any type ofcommunication medium. In some embodiments, the data communicationnetworks are a combination of two or more data communication networks(or sub-networks) coupled to one another. In alternate embodiments,these communication links are implemented using any type ofcommunication medium and any communication protocol.

The database service manager 502, mutable storage 510, executionplatform 512, and storage platform 514 are shown in FIG. 5 as individualcomponents. However, each of database service manager 502, mutablestorage 510, execution platform 512, and storage platform 514 may beimplemented as a distributed system (e.g., distributed across multiplesystems/platforms at multiple geographic locations) or may be combinedinto one or more systems. Additionally, each of the database servicemanager 502, mutable storage 510, the execution platform 512, and thestorage platform 514 may be scaled up or down (independently of oneanother) depending on changes to the requests received from users504-508 and the changing needs of the data processing platform 500.Thus, in the described embodiments, the data processing platform 500 isdynamic and supports regular changes to meet the current data processingneeds.

FIG. 6 illustrates a block diagram depicting components of databaseservice manager 502, according to one embodiment. The database servicemanager 502 includes an access manager 602 and a key manager 604 coupledto a data storage device 606. The access manager 602 handlesauthentication and authorization tasks for the systems described herein.The key manager 604 manages storage and authentication of keys usedduring authentication and authorization tasks. A request processingservice 608 manages received data storage requests and data retrievalrequests. A management console service 610 supports access to varioussystems and processes by administrators and other system managers.

The database service manager 502 also includes an SQL compiler 612, anSQL optimizer 614 and an SQL executor 616. SQL compiler 612 parses SQLqueries and generates the execution code for the queries. SQL optimizer614 determines the best method to execute queries based on the data thatneeds to be processed. SQL executor 616 executes the query code forqueries received by database service manager 502. A query scheduler andcoordinator 618 sends received queries to the appropriate services orsystems for compilation, optimization, and dispatch to an executionplatform 612. A virtual warehouse manager 620 manages the operation ofmultiple virtual warehouses.

Additionally, the database service manager 502 includes a changetracking manager 628, which manages the information related to the datastored in the remote data storage devices and in the local caches. Amonitor and workload analyzer 624 oversees the processes performed bythe database service manager 502 and manages the distribution of tasks(e.g., workload) across the virtual warehouses and execution nodes inthe execution platform 512. Change tracking manager 628 and monitor andworkload analyzer 624 are coupled to a data storage device 626. In oneembodiment, the configuration and metadata manger 622 collects, stores,and manages metadata in an immutable storage resource. In oneembodiment, updates to metadata result in new files and are not updatedin place.

Metadata files, as discussed herein, may include files that containmetadata of modifications (e.g., each modification) to any databasetable in a data warehouse. A modification of a database table maygenerate one or more metadata files, often just a single metadata file.In one embodiment, metadata files contain the following information:information about a metadata file, including a version number; a list ofall added table data files; a list of deleted table data files; andinformation about each added table data file, including file path, filesize, file key id, as well as summaries of all rows and columns that arestored in the table data file.

In one embodiment, the contents of metadata files may vary over time. Ifformat or content of a metadata file changes, the version number of themetadata file may be incremented. In one embodiment, the metadata store(or other mutable data storage resource) only stores information aboutmetadata files (which are stored in immutable storage), not about tabledata files. In practice, information about metadata files stored in inthe metadata store (or other mutable storage) is very limited and maycontain data for thousands of metadata files. In one embodiment,information for up to 30,000 metadata files may be stored in metadatastore or other mutable storage. This dramatically reduces the amount ofstorage needed in the metadata store or other mutable storage.

In one embodiment, a system writes metadata files to cloud storage forevery modification of a database table (e.g., modification of table datafiles). In addition to adding and deleting files, every modification toa database table in the data warehouse also generates one or moremetadata files. Typically, a modification creates a single metadatafile. However, if the modification to the table is large (e.g., aninsert into a table that produces very many files), it may result in thecreation of multiple metadata files. Further operation of the changetracking manager 628 will be discussed further in relation to FIGS.6-12.

The database service manager 502 also includes a change tracking manager628, which manages the generation of change tracking history such as oneor more change tracking columns stored in a table. The change trackingmanager 628 further manages the generation of a delta report indicatinga total change that has occurred on a database table between a firsttimestamp and a second timestamp. Because multiple users/systems mayaccess the same data simultaneously, changes to the data may besynchronized to ensure that each user/system is working with the currentversion of the data and has access to a change tracking history for thedata.

Security improvements are also implemented in some embodiments. In oneembodiment, metadata files and change tracking information is encryptedusing individual file keys. Within a micro-partition, columns may beencrypted individually using AES-CTR mode with different start counters.This allows a database system to read an individual column from amicro-partition because it can be decrypted without needing to decryptthe whole micro-partition at once. Encryption improves security becausenobody can read the micro-partition without having the proper file key.

For verification that a micro-partition has not been altered, the systemmay store hashes of columns for each column within the micro-partition.Before decrypting the data, the system compares the hash of theencrypted column with the stored hash of the column of thismicro-partition. If the hashes do not match, the micro-partition musthave been altered. This improves security because all altering ofmicro-partitions is detected by the database system.

FIG. 7 is a schematic block diagram illustrating components of a changetracking manager 628, according to one embodiment. The change trackingmanager 628 may collect, store, and manage metadata about table datafiles (i.e. micro-partitions) as well as metadata about metadata files.Such metadata includes change tracking information or a table historyincluding a log of changes that have occurred on a table. The changetracking manager 628 includes a table data component 702, a metadatacomponent 704, a transaction data component 706, a modification datacomponent 708, a joining component 710, a change tracking component 712,a querying component 714, an encryption component 716, and a reportingcomponent 718. The components 702-718 are given by way of illustrationonly and may not all be included in all embodiments. In fact, someembodiments may include only one or any combination of two or more ofthe components 702-718. For example, some of the components may belocated outside or separate from the change tracking manager 628, suchas within a database service manager 502 or processing platform 500.Furthermore, the components 702-718 may comprise hardware, computerreadable instructions, or a combination of both to perform thefunctionality and provide the structures discussed herein.

The table data component 702 stores table data for a database, the tabledata includes information in rows and columns of one or more databasetables. The table data component 702 may store table data inmicro-partitions within a storage resource. Example storage resourcesinclude cloud storage and/or immutable storage. In one embodiment, thestorage resources for storage of table data files may be dynamicallyallocated to accommodate increases or decreases in storage requirement.The table data component 702 may manage and store table data by causingthe data to be stored or updated in a remote resource, such as a cloudstorage resource or service.

The metadata component 704 stores metadata on immutable storage such asa micro-partition. The metadata may include information about ordescribing the table data for the database stored by the table datacomponent 702. In one embodiment, the metadata files may includemetadata such as an indication of added or deleted table data files. Themetadata may include file information for table data files, the fileinformation including one or more of a file name and a storage location.In one embodiment, the metadata may be stored in files on the same cloudstorage resources as the table data. In one embodiment, metadatacomponent 704 may cause the metadata to be stored within metadata filesin a column-by-column format in remote cloud storage.

The metadata component 704 may also collect and manage storage ofmetadata within metadata files on the immutable storage. The metadatacomponent 704 may create, in response to a change in the table data, anew metadata file in the immutable storage without modifying previousmetadata files. The new metadata file may include metadata indicatingthe change in the table data. In one embodiment, the metadata in the newmetadata file indicates an addition or a deletion of a table data filecomprising the table data. The metadata component 704 may also deleteexpired metadata files. Expired metadata files may include those olderthan a specific age and that are not referenced in metadata informationstored by the change tracking history component 706.

The transaction data component 706 generates and stores transaction datafor each transaction that is executed on a table. The transaction datacomponent 706 may associate the transaction data with a newmicro-partition such that the transaction data is stored as metadata inthe new micro-partition. Such transaction data may include, for example,an identity of a user or account that initiated a DML or SQL statement,when the transaction was requested, when the transaction was initiated,when the transaction was completed, how the transaction impacted thetable, what rows and/or micro-partitions were modified by thetransaction, and so forth.

The modification data component 708 stores and manages information aboutchanges made to the table data. The modification data may be stored inlocal mutable storage and/or within the table data as a change trackingcolumn, for example. In one embodiment, the modification data may bestored and updated in-place. In one embodiment, the modification data isstored within an immutable micro-partition in a change tracking columnindicating a most recent change that occurred on a row and/or a log ofchanges that have occurred on the table. In an embodiment, themodification data component 708 secures a timestamp to a transactionthat occurred on the table and further secures a timestamp to eachchange or modification that occurs on one or more rows of the table.

The joining component 710 joins transaction data with modification data.The joining component 710 may store the joined data as metadata within anew micro-partition. The joined data may be stored in local mutablestorage and/or within the table data in a column, for example.

The change tracking component 712 determines and stores a lineage ofmodifications made to a table. The lineage may be stored in localmutable storage and/or within the table data such as a change trackingcolumn, for example. The lineage may include joined data or modificationdata. The lineage may be queried to determine either of a deltaindicating a net change between a first timestamp and a second timestampand/or a comprehensive change tracking summary indicating all changesthat occurred on the table between the first timestamp and the secondtimestamp.

The querying component 714 may run a single query to determine what rowsand/or micro-partitions in a table have been changed and furtherdetermine what transactions caused each change to the table. Thequerying component may run the query on any of the transaction data, themodification data, and/or the joined data to determine a comprehensivechange tracking summary for the table. The querying component 714 may beutilized to greatly reduce the cost for determining the comprehensivechange tracking summary for the table by negating the need to determinea change between a plurality of sequential pairs of table versions.

The encryption component 716 is configured to encrypt table data andmetadata. In one embodiment, the encryption component 716 encrypts themetadata column-by-column to allow for independent decryption andreading of metadata for a specific column.

The reporting component 718 generates a report based on data determinedby the querying component 714. The report may include a comprehensivesummary of all transactions that have been executed on a table, and howthose transaction modified the time, between two timestamps. The reportmay further include, for example, an indication of when each of thetransactions and/or intermediate modifications to the table occurred, anindication of what transactions caused each intermediate modification onthe table, an indication of what rows of the table were modified by whattransaction, an indication of what user account initiated a transactionthat caused a modification on the table, and so forth.

FIG. 8 is a schematic flow chart diagram illustrating an example method800 for determining a series of changes made to a database table. Themethod 800 may be performed by a change tracking manager 628, databaseservice manager 502, processing platform 500, and/or other service orplatform.

The method 800 begins and a computing device executes at 802 atransaction to modify data in a micro-partition of a table of a databaseby generating a new micro-partition that reflects the transaction. Thecomputing device associates at 804 transaction data with the newmicro-partition, wherein the transaction data comprises a timestamp whenthe transaction was fully executed. The computing device associates at806 modification data with the new micro-partition that comprises anindication of one or more rows of the table that were modified by thetransaction. The computing device joins at 808 the transaction data withthe modification data to generate joined data. The computing devicequeries at 810 the joined data to determine a listing of intermediatemodifications made to the table between a first timestamp and a secondtimestamp.

FIG. 9 is a schematic flow chart diagram illustrating an example method900 for determining a series of changes made to a database table. Themethod 900 may be performed by a change tracking manager 628, databaseservice manager 502, processing platform 500, and/or other service orplatform.

The method 900 begins and a computing device executes at 902 atransaction to modify data in a micro-partition of a table of a databaseby generating a new micro-partition that reflects the transaction andremoving the micro-partition after the new micro-partition is fullygenerated. The computing device associates at 904 transaction data withthe new micro-partition, wherein the transaction data comprises atimestamp when the transaction was fully executed. The computing deviceassociates at 906 modification data with the new micro-partition thatcomprises an indication of one or more rows of the table that weremodified by the transaction. The computing device joins at 908 thetransaction data with the modification data to generate joined data. Thecomputing device queries at 910 the joined data to determine a listingof intermediate modifications made to the table between a firsttimestamp and a second timestamp by deriving tuple granularity changesbetween each of a series of sequential micro-partition pairs between thefirst timestamp and the second timestamp. The computing device generatesat 912 a report comprising the listing of intermediate modificationsmade to the table between the first timestamp and the second timestamp.

FIG. 10 is a block diagram depicting an example computing device 1000.In some embodiments, computing device 1000 is used to implement one ormore of the systems and components discussed herein. For example,computing device 1000 may include or be part of a change trackingmanager 628, a database service manager 502, a processing platform 500,and/or any other components or systems discussed herein. As anotherexample, the components, systems, or platforms discussed herein mayinclude one or more computing devices 1000. Further, computing device1000 may interact with any of the systems and components describedherein. Accordingly, computing device 1000 may be used to performvarious procedures and tasks, such as those discussed herein. Computingdevice 1000 can function as a server, a client or any other computingentity. Computing device 1000 can be any of a wide variety of computingdevices, such as a desktop computer, a notebook computer, a servercomputer, a handheld computer, a tablet, and the like.

Computing device 1000 includes one or more processor(s) 1002, one ormore memory device(s) 1004, one or more interface(s) 1006, one or moremass storage device(s) 1008, and one or more Input/Output (I/O)device(s) 1010, all of which are coupled to a bus 1012. Processor(s)1002 include one or more processors or controllers that executeinstructions stored in memory device(s) 1004 and/or mass storagedevice(s) 1008. Processor(s) 1002 may also include various types ofcomputer-readable media, such as cache memory.

Memory device(s) 1004 include various computer-readable media, such asvolatile memory (e.g., random access memory (RAM)) and/or nonvolatilememory (e.g., read-only memory (ROM)). Memory device(s) 1004 may alsoinclude rewritable ROM, such as Flash memory.

Mass storage device(s) 1008 include various computer readable media,such as magnetic tapes, magnetic disks, optical disks, solid statememory (e.g., Flash memory), and so forth. Various drives may also beincluded in mass storage device(s) 1008 to enable reading from and/orwriting to the various computer readable media. Mass storage device(s)1008 include removable media and/or non-removable media.

I/O device(s) 1010 include various devices that allow data and/or otherinformation to be input to or retrieved from computing device 1000.Example I/O device(s) 1010 include cursor control devices, keyboards,keypads, microphones, monitors or other display devices, speakers,printers, network interface cards, modems, lenses, CCDs or other imagecapture devices, and the like.

Interface(s) 1006 include various interfaces that allow computing device1000 to interact with other systems, devices, or computing environments.Example interface(s) 1006 include any number of different networkinterfaces, such as interfaces to local area networks (LANs), wide areanetworks (WANs), wireless networks, and the Internet.

Bus 1012 allows processor(s) 1002, memory device(s) 1004, interface(s)1006, mass storage device(s) 1008, and I/O device(s) 1010 to communicatewith one another, as well as other devices or components coupled to bus1012. Bus 1012 represents one or more of several types of busstructures, such as a system bus, PCI bus, USB bus, and so forth.

Examples

The following examples pertain to further embodiments.

Example 1 is a method for tracking incremental changes to database data.The method includes executing a transaction to modify data in amicro-partition of a table of a database by generating a newmicro-partition that embodies the transaction. The method includesassociating transaction data with the new micro-partition, wherein thetransaction data comprises a timestamp when the transaction was fullyexecuted and associating modification data with the new micro-partitionthat comprises an indication of one or more rows of the table that weremodified by the transaction. The method includes joining the transactiondata with the modification data to generated joined data. The methodincludes querying the joined data to determine a listing of intermediatemodifications made to the table between a first timestamp and a secondtimestamp.

Example 2 is a method as in Example 1, wherein querying the joined datacomprises querying a plurality of entries of joined data for a pluralityof transactions executed on the table between the first timestamp andthe second timestamp.

Example 3 is a method as in any of Examples 1-2, wherein the transactioncomprises one or more of: a delete command, an insert command, an updatecommand, or a merge command.

Example 4 is a method as in any of Examples 1-3, wherein executing thetransaction further comprises removing the micro-partition after the newmicro-partition is fully generated.

Example 5 is a method as in any of Examples 1-4, wherein associating thetransaction data with the new micro-partition comprises inserting thetransaction data in a transaction tracking column in the newmicro-partition, and wherein associating the modification data with thenew micro-partition comprises inserting the modification data in achange tracking column in the new micro-partition.

Example 6 is a method as in any of Examples 1-5, wherein themodification data comprises one or more of: a prior micro-partitionidentification for a value in the table, a prior row identification fora value in the table, a transaction that occurred on a row of the table,or an indication of whether a value of the table was updated.

Example 7 is a method as in any of Examples 1-6, wherein querying thejoined data comprises deriving tuple granularity changes between each ofa series of sequential micro-partition pairs between the first timestampand the second timestamp to determine a series of intermediatemodifications made to the table between the first timestamp and thesecond timestamp, and wherein each of the series of sequentialmicro-partition pairs is ordered according to timestamps.

Example 8 is a method as in any of Examples 1-7, wherein the associatingtransaction data with the new micro-partition occurs only after the newmicro-partition is fully generated and the transaction is fullyexecuted.

Example 9 is a method as in any of Examples 1-8, wherein the transactionmodifies rows of the table that are stored across a plurality ofmicro-partitions of the table, and wherein executing the transactioncomprises generating a plurality of new micro-partitions and removingthe plurality of micro-partitions only after the transaction is fullyexecuted.

Example 10 is a method as in any of Examples 1-9, further comprisinggenerating a report comprising one or more of: the listing ofintermediate modifications made to the table between the first timestampand the second timestamp; an indication of when each of the intermediatemodifications occurred; an indication of what transaction caused each ofthe intermediate modifications; an indication of what rows of the tablewere modified by a transaction that initiated a modification to thetable; or an indication of what user account initiated a transactionthat initiated a modification to the table.

Example 11 is a system for tracking intermediate changes to databasedata. The system includes means for executing a transaction to modifydata in a micro-partition of a table of a database by generating a newmicro-partition that embodies the transaction. The system includes meansfor associating transaction data with the new micro-partition, whereinthe transaction data comprises a timestamp when the transaction wasfully executed. The system includes means for associating modificationdata with the new micro-partition that comprises an indication of one ormore rows of the table that were modified by the transaction. The systemincludes means for joining the transaction data with the modificationdata to generated joined data. The system includes means for queryingthe joined data to determine a listing of incremental modifications madeto the table between a first timestamp and a second timestamp.

Example 12 is a system as in Example 11, wherein the means for queryingthe joined data is configured to query a plurality of entries of joineddata for a plurality of transactions executed on the table between thefirst timestamp and the second timestamp.

Example 13 is a system as in any of Examples 11-12, wherein the meansfor executing the transaction is further configured to remove themicro-partition from the database after the new micro-partition is fullygenerated.

Example 14 is a system as in any of Examples 11-13, wherein the meansfor associating the transaction data with the new micro-partition isconfigured to insert the transaction data in a transaction trackingcolumn in the new micro-partition, and wherein the means for associatingthe modification data with the new micro-partition is configured toinsert the modification data in a change tracking column in the newmicro-partition, and wherein the modification data comprises one or moreof: a prior micro-partition identification for a value in the table, aprior row identification for a value in the table, a transaction thatoccurred on a row of the table, or an indication of whether a value ofthe table was updated.

Example 15 is a system as in any of Examples 11-14, wherein the meansfor querying the joined data is configured to derive tuple granularitychanges between each of a series of sequential micro-partition pairsbetween the first timestamp and the second timestamp to determine aseries of intermediate modifications made to the table between the firsttimestamp and the second timestamp, and wherein each of the series ofsequential micro-partition pairs is ordered according to timestamps.

Example 16 is a system as in any of Examples 11-15, further comprisingmeans for generating a report comprising one or more of: the listing ofintermediate modifications made to the table between the first timestampand the second timestamp; an indication of when each of the intermediatemodifications occurred; an indication of what transaction caused each ofthe intermediate modifications; an indication of what rows of the tablewere modified by a transaction that initiated a modification to thetable; or an indication of what user account initiated a transactionthat initiated a modification to the table.

Example 17 is non-transitory computer readable storage media storinginstructions that, when executed by one or more processors, cause theone or more processors to: execute a transaction to modify data in amicro-partition of a table of a database by generating a newmicro-partition that embodies the transaction; associate transactiondata with the new micro-partition, wherein the transaction datacomprises a timestamp when the transaction was fully executed; associatemodification data with the new micro-partition that comprises anindication of one or more rows of the table that were modified by thetransaction; join the transaction data with the modification data togenerated joined data; and query the joined data to determine a listingof intermediate modifications made to the table between a firsttimestamp and a second timestamp.

Example 18 is non-transitory computer readable storage media as inExample 17, wherein the instructions further cause the one or moreprocessors to execute the transaction by removing the micro-partitionfrom the database after the new micro-partition is fully generated.

Example 19 is non-transitory computer readable storage media as in anyof Examples 17-18, wherein the instructions cause the one or moreprocessors to associate the transaction data with the newmicro-partition by inserting the transaction data in a transactiontracking column in the new micro-partition, and wherein the instructionscause the one or more processors to associate the modification data withthe new micro-partition by inserting the modification data in a changetracking column in the new micro-partition, and wherein the modificationdata comprises one or more of: a prior micro-partition identificationfor a value in the table, a prior row identification for a value in thetable, a transaction that occurred on a row of the table, or anindication of whether a value of the table was updated.

Example 20 is non-transitory computer readable storage media as in anyof Examples 17-19, wherein the instructions cause the one or moreprocessors to query the joined data by deriving tuple granularitychanges between each of a series of sequential micro-partition pairsbetween the first timestamp and the second timestamp to determine aseries of intermediate modifications made to the table between the firsttimestamp and the second timestamp, and wherein each of the series ofsequential micro-partition pairs is ordered according to timestamps.

Example 21 is non-transitory computer readable storage media as in anyof Examples 17-20, wherein the instructions further cause the one ormore processors to generate a report comprising one or more of: thelisting of intermediate modifications made to the table between thefirst timestamp and the second timestamp; an indication of when each ofthe intermediate modifications occurred; an indication of whattransaction caused each of the intermediate modifications; an indicationof what rows of the table were modified by a transaction that initiateda modification to the table; or an indication of what user accountinitiated a transaction that initiated a modification to the table.

Example 22 is an apparatus including means to perform a method as in anyof Examples 1-10.

Example 23 is a machine-readable storage including machine-readableinstructions that, when executed, implement a method or realize anapparatus of any of Examples 1-10.

The flow diagrams and block diagrams herein illustrate the architecture,functionality, and operation of possible implementations of systems,methods, and computer program products according to various embodimentsof the present disclosure. In this regard, each block in the flowdiagrams or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It will also be notedthat each block of the block diagrams and/or flow diagrams, andcombinations of blocks in the block diagrams and/or flow diagrams, maybe implemented by special purpose hardware-based systems that performthe specified functions or acts, or combinations of special purposehardware and computer instructions. These computer program instructionsmay also be stored in a computer-readable medium that can direct acomputer or other programmable data processing apparatus to function ina particular manner, such that the instructions stored in thecomputer-readable medium produce an article of manufacture includinginstruction means which implement the function/act specified in the flowdiagram and/or block diagram block or blocks.

The systems and methods described herein provide a flexible and scalabledata warehouse using new data processing platforms, methods, systems,and algorithms. In some embodiments, the described systems and methodsleverage a cloud infrastructure that supports cloud-based storageresources, computing resources, and the like. Example cloud-basedstorage resources offer significant storage capacity available on-demandat a low cost. Further, these cloud-based storage resources may befault-tolerant and highly scalable, which can be costly to achieve inprivate data storage systems. Example cloud-based computing resourcesare available on-demand and may be priced based on actual usage levelsof the resources. Typically, the cloud infrastructure is dynamicallydeployed, reconfigured, and decommissioned in a rapid manner.

In the described systems and methods, a data storage system utilizes anSQL (Structured Query Language)-based relational database. However,these systems and methods are applicable to any type of database usingany data storage architecture and using any language to store andretrieve data within the database. The systems and methods describedherein may also provide a multi-tenant system that supports isolation ofcomputing resources and data between different customers/clients andbetween different users within the same customer/client.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, a non-transitorycomputer readable storage medium, or any other machine readable storagemedium wherein, when the program code is loaded into and executed by amachine, such as a computer, the machine becomes an apparatus forpracticing the various techniques. In the case of program code executionon programmable computers, the computing device may include a processor,a storage medium readable by the processor (including volatile andnon-volatile memory and/or storage elements), at least one input device,and at least one output device. The volatile and non-volatile memoryand/or storage elements may be a RAM, an EPROM, a flash drive, anoptical drive, a magnetic hard drive, or another medium for storingelectronic data. One or more programs that may implement or utilize thevarious techniques described herein may use an application programminginterface (API), reusable controls, and the like. Such programs may beimplemented in a high-level procedural or an object-oriented programminglanguage to communicate with a computer system. However, the program(s)may be implemented in assembly or machine language, if desired. In anycase, the language may be a compiled or interpreted language, andcombined with hardware implementations.

It should be understood that many of the functional units described inthis specification may be implemented as one or more components, whichis a term used to more particularly emphasize their implementationindependence. For example, a component may be implemented as a hardwarecircuit comprising custom very large-scale integration (VLSI) circuitsor gate arrays, off-the-shelf semiconductors such as logic chips,transistors, or other discrete components. A component may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices, orthe like.

Components may also be implemented in software for execution by varioustypes of processors. An identified component of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object, aprocedure, or a function. Nevertheless, the executables of an identifiedcomponent need not be physically located together but may comprisedisparate instructions stored in different locations that, when joinedlogically together, comprise the component and achieve the statedpurpose for the component.

Indeed, a component of executable code may be a single instruction, ormany instructions, and may even be distributed over several differentcode segments, among different programs, and across several memorydevices. Similarly, operational data may be identified and illustratedherein within components and may be embodied in any suitable form andorganized within any suitable type of data structure. The operationaldata may be collected as a single data set or may be distributed overdifferent locations including over different storage devices, and mayexist, at least partially, merely as electronic signals on a system ornetwork. The components may be passive or active, including agentsoperable to perform desired functions.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentdisclosure. Thus, appearances of the phrase “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based onits presentation in a common group without indications to the contrary.In addition, various embodiments and examples of the present disclosuremay be referred to herein along with alternatives for the variouscomponents thereof. It is understood that such embodiments, examples,and alternatives are not to be construed as de facto equivalents of oneanother but are to be considered as separate and autonomousrepresentations of the present disclosure.

Although the foregoing has been described in some detail for purposes ofclarity, it will be apparent that certain changes and modifications maybe made without departing from the principles thereof. It should benoted that there are many alternative ways of implementing both theprocesses and apparatuses described herein. Accordingly, the presentembodiments are to be considered illustrative and not restrictive.

Those having skill in the art will appreciate that many changes may bemade to the details of the above-described embodiments without departingfrom the underlying principles of the disclosure. The scope of thepresent disclosure should, therefore, be determined only by thefollowing claims.

What is claimed is:
 1. A method comprising: providing a firstmicro-partition in a table at a first timestamp, the firstmicro-partition storing data; receiving instructions for a transactionrelated to the stored data in the first micro-partition; in response tothe instructions, generating transaction data associated with theinstructions and performing multiple modifications to the stored data togenerate a second micro-partition and remove the first micro-partitionfrom the table, the second micro-partition being generated at a secondtimestamp; generating a delta table, the delta table storing finalchanges to the stored data in the second micro-partition at the secondtimestamp from the first micro-partition at the first timestamp;generating modification data, the modification data tracking themodifications performed to the stored data between the first and secondtimestamps; and joining the modification data with the transaction datato generate joined data, the joined data indicating intermediate changesto the stored data between the first and second timestamps.
 2. Themethod of claim 1, further comprising: querying the joined data; andgenerating a listing of the intermediate changes.
 3. The method of claim2, wherein querying the joined data includes calculating tuple changesbetween each of a series of sequential micro-partition pairs between thefirst and second timestamps.
 4. The method of claim 1, furthercomprising: performing multiple modifications to a row of a plurality ofrows in the first micro-partition, wherein the delta table stores aninitial value of the row at the first timestamp and a final value of therow after performance of the multiple modifications to the row at thesecond timestamp, and wherein the joined data indicates at least oneintermediate change to the row between the initial and final values. 5.The method of claim 1, wherein the delta table includes informationindicating which rows have been modified, final values of rows that havebeen modified between the first and second timestamps, and an actiontype of the modification for each row modified.
 6. The method of claim1, further comprising: storing the transaction data in the secondmicro-partition as metadata, wherein the transaction data includes oneor more of: an identity of an account that initiated the transaction,the second time stamp, a third timestamp when the transaction wasrequested, a fourth timestamp when execution of the transaction began, alisting of all rows that were modified by the transaction, and detailsof the modifications.
 7. The method of claim 1, further comprising:storing the modification data in the second micro-partition as metadata,wherein the modification data includes a lineage of modifications madeto the table.
 8. The method of claim 1, further comprising: storing thetransaction data and the modification data in the second micro-partitionas metadata, wherein the metadata is stored in immutable storage.
 9. Themethod of claim 1, further comprising: storing the transaction data andthe modification data in the second micro-partition as metadata, whereinthe metadata is stored in mutable storage.
 10. A system comprising: oneor more processors of a machine; and a memory storing instructions that,when executed by the one or more processors, cause the machine toperform operations comprising: providing a first micro-partition in atable at a first timestamp, the first micro-partition storing data;receiving instructions for a transaction related to the stored data inthe first micro-partition; in response to the instructions, generatingtransaction data associated with the instructions and performingmultiple modifications to the stored data to generate a secondmicro-partition and remove the first micro-partition from the table, thesecond micro-partition being generated at a second timestamp; generatinga delta table, the delta table storing final changes to the stored datain the second micro-partition at the second timestamp from the firstmicro-partition at the first timestamp; generating modification data,the modification data tracking the modifications performed to the storeddata between the first and second timestamps; and joining themodification data with the transaction data to generate joined data, thejoined data indicating intermediate changes to the stored data betweenthe first and second timestamps.
 11. The system of claim 10, theoperations further comprising: querying the joined data; and generatinga listing of the intermediate changes.
 12. The system of claim 11,wherein querying the joined data includes calculating tuple changesbetween each of a series of sequential micro-partition pairs between thefirst and second timestamps.
 13. The system of claim 10, the operationsfurther comprising: performing multiple modifications to a row of aplurality of rows in the first micro-partition, wherein the delta tablestores an initial value of the row at the first timestamp and a finalvalue of the row after performance of the multiple modifications to therow at the second timestamp, and wherein the joined data indicates atleast one intermediate change to the row between the initial and finalvalues.
 14. The system of claim 10, wherein the delta table includesinformation indicating which rows have been modified, final values ofrows that have been modified between the first and second timestamps,and an action type of the modification for each row modified.
 15. Thesystem of claim 10, the operations further comprising: storing thetransaction data in the second micro-partition as metadata, wherein thetransaction data includes one or more of: an identity of an account thatinitiated the transaction, the second time stamp, a third timestamp whenthe transaction was requested, a fourth timestamp when execution of thetransaction began, a listing of all rows that were modified by thetransaction, and details of the modifications.
 16. The system of claim10, the operations further comprising: storing the modification data inthe second micro-partition as metadata, wherein the modification dataincludes a lineage of modifications made to the table.
 17. The system ofclaim 10, the operations further comprising: storing the transactiondata and the modification data in the second micro-partition asmetadata, wherein the metadata is stored in immutable storage.
 18. Thesystem of claim 10, the operations further comprising: storing thetransaction data and the modification data in the second micro-partitionas metadata, wherein the metadata is stored in mutable storage.
 19. Anon-transitory computer readable storage media storing instructionsthat, when executed by one or more processors, cause the one or moreprocessors to: providing a first micro-partition in a table at a firsttimestamp, the first micro-partition storing data; receivinginstructions for a transaction related to the stored data in the firstmicro-partition; in response to the instructions, generating transactiondata associated with the instructions and performing multiplemodifications to the stored data to generate a second micro-partitionand remove the first micro-partition from the table, the secondmicro-partition being generated at a second timestamp; generating adelta table, the delta table storing final changes to the stored data inthe second micro-partition at the second timestamp from the firstmicro-partition at the first timestamp; generating modification data,the modification data tracking the modifications performed to the storeddata between the first and second timestamps; and joining themodification data with the transaction data to generate joined data, thejoined data indicating intermediate changes to the stored data betweenthe first and second timestamps.
 20. The non-transitory computerreadable storage media of claim 19, further comprising: querying thejoined data; and generating a listing of the intermediate changes. 21.The non-transitory computer readable storage media of claim 20, whereinquerying the joined data includes calculating tuple changes between eachof a series of sequential micro-partition pairs between the first andsecond timestamps.
 22. The non-transitory computer readable storagemedia of claim 19, further comprising: performing multiple modificationsto a row of a plurality of rows in the first micro-partition, whereinthe delta table stores an initial value of the row at the firsttimestamp and a final value of the row after performance of the multiplemodifications to the row at the second timestamp, and wherein the joineddata indicates at least one intermediate change to the row between theinitial and final values.
 23. The non-transitory computer readablestorage media of claim 19, wherein the delta table includes informationindicating which rows have been modified, final values of rows that havebeen modified between the first and second timestamps, and an actiontype of the modification for each row modified.
 24. The non-transitorycomputer readable storage media of claim 19, further comprising: storingthe transaction data in the second micro-partition as metadata, whereinthe transaction data includes one or more of: an identity of an accountthat initiated the transaction, the second time stamp, a third timestampwhen the transaction was requested, a fourth timestamp when execution ofthe transaction began, a listing of all rows that were modified by thetransaction, and details of the modifications.
 25. The non-transitorycomputer readable storage media of claim 19, further comprising: storingthe modification data in the second micro-partition as metadata, whereinthe modification data includes a lineage of modifications made to thetable.
 26. The non-transitory computer readable storage media of claim19, further comprising: storing the transaction data and themodification data in the second micro-partition as metadata, wherein themetadata is stored in immutable storage.
 27. The non-transitory computerreadable storage media of claim 19, further comprising: storing thetransaction data and the modification data in the second micro-partitionas metadata, wherein the metadata is stored in mutable storage.